Mm you think!
when he was crying with yanek his eyes was gold!
I think is just the author forgot to paint xD
They weren't super gold though, they were still sort of gray...like his eyes are super amber almost glowing when he is with Ein
Yesss!!
I think Diesel's eyes turn amber when he is feeling highly emotional. It occurred mostly in the presence of Ein, only after he has done something considerate that struck a deep chord in Diesel.
However it also happened in chapter 53, during the interaction with Yanek. The author is subtly telling us that Diesel was really upset in that occasion.
Read the flashback over and pay attention to Diesel's eye color. Majority of the time when he is with or around Yanek, his eyes are silver/gray. However, when he is around Ein or looking at Ein, his true eye color is shown--bright amber almost gold. I feel like the author did this on purpose.